It is known that when designing a wrench, the torque value of the wrench must be tested and measured as the basis for the structural design of the wrench.
U.S. Pat. Nos. 5,911,154 and 6,772,645 designed by the inventor disclose torque meters for testing and measuring torque of a wrench. The conventional torque meter has a housing, an operation shaft and a flexible beam. The operation shaft and the flexible beam are installed in the housing. One end of the flexible beam is inserted in the operation shaft. A dial gauge is mounted on a top face of the housing. A probe of the dial gauge extends into the housing to contact with the flexible beam. When a wrench is fitted on the operation shaft and wrenched, the flexible beam is flexed to push the probe of the dial gauge. The probe then drives an indicator of the dial gauge through an internal mechanism thereof. The indicator then indicates a scale representing the torque value corresponding to the flexure of the flexible beam.
The conventional torque meter has a simply mechanical structure. That is, the whole the torque meter is simply composed of multiple mechanical components including the flexible beam, the probe pushed by the flexible beam, the internal mechanism pushed by the probe and the indicator driven by the internal mechanism. These components cooperate to show the torque value in a mechanical manner. Each of these components has a mechanical tolerance. The more the number of the components is, the large the total mechanical tolerance is. As a result, the error of the measured data is increased to lower the precision. Also, the sensitivity of the torque meter is affected.
Moreover, an operator needs to wrench the wrench on one hand and at the same time watch the scale of the gauge on the other hand. Therefore, it is quite difficult for the operator to read the scale representing the torque value, which is indicated by the indicator. The experiences tell that when watching the gauge, the observed value often varies with the watching height and angle. Furthermore, it is hard to clearly and precisely read the value behind the decimal point.